The Effect of Vitamin D3 Supplementation on the Incidence of Diagnosed Dementia Among Healthy Older Adults-The Finnish Vitamin D Trial

BACKGROUND: Some short-term vitamin D supplementation trials suggest benefits on cognitive performance, but apart from observational studies, there is little evidence whether long-term vitamin D supplementation can prevent development of dementia. We investigated whether vitamin D3 supplementation could affect the incidence of diagnosed dementia in a generally healthy population. METHODS: The study included 2 492 participants from the Finnish Vitamin D Trial, free of diagnosed dementia at baseline. They were randomized to placebo, 1 600 IU/d, or 3 200 IU/d of vitamin D3 arm for up to 5 years. Incident diagnoses of dementia were obtained from the national care registries. RESULTS: The mean age of the participants at baseline was 68.2 years and 42.8% were female. During the mean follow-up of 4.2 years, 18 participants in the placebo arm, 14 participants in the 1 600 IU/d arm (compared to placebo, hazard ratio [HR] = 0.77, 95% confidence interval [CI]: 0.38-1.55), and 13 participants in the 3 200 IU/d arm (HR = 0.72, 95% CI: 0.35-1.48) were diagnosed with dementia. Of the diagnoses, 29 were Alzheimer's disease, without statistically significant differences in the event rates between the 3 arms. Age, sex, or body mass index did not modify the effects. In the subgroup of 550 participants, the mean baseline serum 25-hydroxyvitamin D concentration was 74.8 nmol/L. After 12 months, the mean concentrations were 73.0, 99.7, and 120.4 nmol/L in the placebo, 1 600 IU/d, and 3 200 IU/d arms, respectively. CONCLUSIONS: Five-year, medium-dose or high-dose vitamin D3 supplementation did not affect the dementia incidence in this largely vitamin D-sufficient older population. CLINICAL TRIAL REGISTRY NUMBER: ClinicalTrials.gov: NCT01463813, https://clinicaltrials.gov/ct2/show/NCT01463813.